In recent years, PTT (Push-To-Talk) service has been introduced as one of the voice call services in which one radio communication terminal (cellular phones and the like) can simultaneously communicate with multiple radio communication terminals (group talk) in the same way as a conventional transceiver (see, for example, Patent Document 1). In the PTT service, when one user among the multiple radio communication terminals participating in the group talk speaks while pressing a button on the user's terminal, voice data related to the speech is transmitted to the other radio communication terminals that participate in the group talk.
Meanwhile, the PTT service using SIP (Session Initiation Protocol) has started to provide a service for displaying the identification information of multiple radio communication terminals already participating in a group talk (member identification information such as phone numbers, IP addresses or user names) on a destination terminal that is about to join the group talk.
More specifically, first of all, any ones terminal (originating terminal) among the multiple radio communication terminals (for example, radio communication terminals #A, #B and #C) that already participate in a group talk transmits a call request (INVITE Request) to a SIP server to call out a destination terminal that has not yet participated in the group talk.
Then, on the basis of the call request (INVITE Request) received from the originating terminal, the SIP server generates a call request (INVITE Request) for the destination terminal. The SIP server transmits the generated call request (INVITE Request) to the destination terminal after the completion of a login processing such as registering the location of the destination terminal in response to the request from the destination terminal.
With such processing, the destination terminal displays the member identification information included in the call request (INVITE Request) received from the SIP server (for example, phone numbers and user names of the radio communication terminals #A, #B and #C).
Patent Document 1: Japanese Patent Translation Publication No. 2005-535156